Despite a law delaying the switch to digital television until June, hundreds of TV stations are planning to turn off their analog signals on Tuesday, potentially leaving millions of unprepared viewers in the dark.

On Wednesday, President Obama signed a bill to delay the nationwide switch from analog to digital television to June 12. The long-planned switch was scheduled for Feb. 17, but a federal program to help subsidize the cost of digital-converter boxes with coupons ran out of money, leaving little time for consumers to get ready for the changeover.

"Millions of Americans, including those in our most vulnerable communities, would have been left in the dark if the conversion had gone on as planned, and this solution is an important step forward as we work to get the nation ready for digital TV," the president said in a statement.

Many viewers may still be left in the dark. With the approval of the Federal Communications Commission, 421 stations still plan to make the transition on Tuesday.

But the FCC has told 106 stations previously approved for the Feb. 17 switch that they now can't shut off their analog signals unless they agree to certain conditions.

Many of these stations are in what the FCC terms "vulnerable markets" — television viewing areas where all of the major network affiliates planned to turn off their analog transmitters on Feb. 17 — leaving over-the-air viewers without any local news or access to emergency information.

This week, the FCC announced measures intended to ensure that viewers still watching TV on old analog sets without cable or satellite service will still have access to important information. For example, at least one station in each market will be required to continue to provide analog service with "DTV transition and emergency information, as well as local news and public affairs programming ... for at least 60 days following February 17, 2009," the FCC said.

The Nielsen Co. estimates that more than 6 million households are still not ready for the digital transition. At least one other study puts the number much higher.

A hundred stations — including those in Wilmington, N.C.; Hawaii; and Chico-Redding, Calif. — have already made the transition to DTV.

At a briefing for reporters on Wednesday, Acting FCC Chairman Michael Copps said the FCC under the previous administration "went about its DTV work with what I would call an anemic strategy in the happy but mistaken belief that the transition would somehow take care of itself." He said the commission "awoke" in the last six months, but he still predicted that "dislocation and confusion are coming on Feb. 17."